The invention relates to a vibration roller with at least one roll tire and a double shaft vibration generator arranged therein wherein the motorically driven unbalance shafts thereof are rotatably supported in a common support contained within the roll tire such that their respective axis of rotation extends parallel to the drive axis of the roll tire.
Vibration rollers of this kind are known from European Patent Application 0 530 546 A1. In these known vibration rollers the two unbalance shafts of the double shaft vibration generator extend parallel to one another on opposite sides of the drive axle of the respective roll tire symmetrically thereto and are rotatably supported in a common generator housing which itself is supported pivotably in a common carrier within the respective roll tire. One of the two unbalance shafts is rotatably driven via gear wheels by a hydraulic drive motor and is coupled with gear wheels to the other drive shaft such that the two unbalance shafts rotate at all times in opposite directions with the same rpm in the generator housing. The flyweights of the two unbalance shafts have the same mass and the same center of gravity spacing so that the vibration generator within the two roll tires produce the same oriented vibration which extends radially to the drive axis of the respective roll tire and the orientation of which depends on the spatial adjustment of the housing of the unbalance shafts.
The solution according to European patent application 0 530 546 A1 is advantageously suitable in connection with soil types which can be compacted best by application of shearing strain and combinations of shearing and compressive strain and it is also well suitable for an economical compaction of relatively great layer thicknesses. Furthermore, a slip produced by the shearing and compressive strain combinations can be counteracted and the traction of the roller can be improved.
The solution according to European Patent Application 0 530 546 A1 has, however, also disadvantages.
In practice, the change of driving orientation takes, especially on bituminous material, approximately 10 to 15 seconds so that for a driving velocity of approximately 5 km/h for the braking process and the subsequent acceleration to 5 km/h in the counter direction a travel distance of 3.5 to 5 m is required. Along this travel distance the vibrator housing is mirror symmetrically adjusted with respect to the vertical plane. This adjustment process causes constantly changing compressive and shearing strain on the soil so that inhomogeneous compaction and undesirable rut formation results. In order to maintain such an inhomogeneous compaction and rut formation within allowable limits, the adjustment process would have to be performed within a fraction of a second which, however, with the known vibration roller is practically not achievable because the vibration generator with respect to the pivot axis has a very large moment of inertia (I=.SIGMA. mr.sup.2) which is caused by the pivotable generator housing itself, by the relatively large distance of the unbalanced shafts from the pivot axis of the generator housing coinciding with the drive axis of the roll tire as well as by the bearing and drive units. For pivoting the generator housing a torque M.sub.d =I* .DELTA.W/.DELTA.t is required. This torque thus increases proportionally with I and the angular acceleration .DELTA.W/.DELTA.t. This means that the shorter the pivoting time is and the greater the moment of inertia I of the generator system, the greater the torque must be. The greater the required torque, the more complicated, however, is the control process.
Furthermore, pivotable generator housings that contain the complete construction of the generator system and the additional pivot bearings require a high technical expenditure and are expensive.
A further disadvantage of the known vibration roller according to European Patent Application 0 530 546 A1 is the unfavorable traction behavior under certain operating conditions.
During compaction process with a vibration roller, that has roll tires with the aforedescribed vibration generators arranged one after another, the roll tire at the forward end in the driving direction has a greater rolling resistance than the rearward one. The hydraulic drive system, provided for both roll tires and switched in parallel, will adjust to the greater required drive moment. For the rearward roller the drive moment is then too large. This favors a slipping of the roller. A possibly provided anti-slip control tries to prevent slip by providing different adjustment angles of the vibration generators in the leading and the rearward roll tire. However, this means that the two roll tires exert different compressive and shearing strain onto the soil which constantly change during driving. This also results in an undesirable inhomogeneous compaction. This inhomogeneous compaction is made even more uncontrollable by the friction coefficient between the roll tire and the soil, by changes of the rolling resistance, and by erroneous driving behavior of the driver.
A further known vibration roller (European Patent Application 053 598 A0) comprises two unbalanced shafts arranged on the roller axle which rotate synchronously with the same rpm, but phase-displaced by 180.degree. relative to one another. The arrangement is such that the vertical forces generator by the unbalanced shafts are compensated, while the oppositely generated horizontal forces produce a torque acting onto the roll tires about the axis of rotation of the roll tire, respectively, the drive axle. This torque exerts an shearing load onto the soil with regard to its absolute value is unchangeable. Tests have shown that this solution is advantageous for the compaction of thin-layer, loose and bituminous material and also leads to advantageous results with respect to the required minimal noise and vibration exposure for the operating personnel. However, this known vibration roller cannot be economically used, in general, for greater layer thickness and for non-loose materials, for example, mixed soils, bonding soils, and rock. Furthermore, the known roller is very prone to slipping, which results in traction problems especially on downslopes or inclines. Also, the known roller according to European Patent Application 053 598 A0 is constructively very complicated because the unbalance shafts must be supported at a great distance from the drive axis of the roll tires for generating the desired torque.
In German Patent Application 32 25 235 A1 a vibration generator arranged within a roller is disclosed which has two concentrically arranged unbalanced shafts that are commonly driven by a hydraulic motor. One unbalanced shaft can be axially displaced by a translatory movement and can be disengaged by a splined shaft clutch in order to adjust it in different rotational positions relative to the other unbalance shaft. In this manner it is possible to increase or decrease the vibration amplitude. This known vibration mechanism is suitable for exerting complex strains onto certain types of soils because the available kinetic energy, as a function of the amplitude adjustment, can be increased and decreased with a square function; however, such amplitude adjusting solutions have certain application-technological disadvantages under certain operating conditions. For example, it is not possible to generate controlled compressive and shearing strain combinations for a homogenous and economical compaction of certain soil types. Furthermore, a metering of the available kinetic energy, which changes as a square function of the amplitude adjustment, is problematic because an erroneous adjustment of the available kinetic energy causes undesirable surface loosening and material destruction for bituminous material with increasing compaction degree. Furthermore, the aforedisclosed known vibration mechanism does not fulfill the requirements with respect to a careful use of the compacting device and a minimal noise and vibration exposure of the operating personnel and the surroundings. Moreover, the known vibration generator is of a complicated construction and prone to breakdown.
In Swiss Patent 271 578 a vibration plate with a vibration generator placed onto the soil contacting plate is represented and disclosed which comprises two coaxially extending unbalance shafts, thus rotating about a common rotational axis, which are adjustable in regard to their respective phase position by a differential among them in opposite rotating direction with synchronous rpm so that it is possible to change the direction of action of the vibration produced by the unbalance shafts relative to the soil contacting plate. The vibration plate can thus be operated so as to move automatically in forward and reverse mode.
German Patent Application 195 39 150 A1 shows and discloses in different embodiments vibration drives for vibration machines that all have coaxially disposed unbalanced shafts. The vibration drives are provided especially for use with vibration jigs and conveying devices. In all embodiments except one the unbalanced shafts are forcedly driven during operation in opposite direction without the possibility of adjusting the relative phase relation. In the one embodiment that differs from the others a drive with the same rotational orientation requires a separate drive for each unbalance shaft which requires a considerable technical expenditure.
Based on the aforementioned prior art, the invention is thus concerned with providing a universally applicable vibration roller that allows, depending on its adjustment, to:
generate about the roll tire axis oscillating rotational vibrations so that primarily shearing strain is exerted onto the soil to be compacted; PA1 introduce at the roll tire axis an oriented force and to adjust the force vector as desired in all directions in order to be able to exert onto the soil to be compacted an optimally combined compressive and shearing strain; or PA1 generate a centrifugal force that is introduced at the roll tire axis and acts in a rotating manner about it and is adjustable in regard to its value in order to exert complex tensions onto the soil to be compacted. PA1 at least one roll tire having a double shaft vibration generator arranged therein; PA1 the double shaft vibration generator comprising a first driven unbalance shaft and a second driven unbalance shaft arranged in the at least one roll tire; PA1 the roll tire having an inner support; PA1 the first and second driven unbalance shafts rotatably supported in the inner support; PA1 the first and second driven unbalance shaft coaxially arranged relative to one another on a common rotational axis such that the second driven unbalance shaft is rotatable about the first driven unbalance shaft; the roll tire having a drive axis; PA1 the common rotational axis of the first and second driven unbalance shafts coinciding with the drive axis of the roll tire; PA1 wherein, for a first operational state of the vibration roller in which a directed vibration is generated, the first and second driven unbalance shaft are coupled such that the first and second driven unbalance shafts rotate in opposite directions to one another and wherein a position angle between a maximum resulting centrifugal force (force vector) and a travel direction of the vibration roller is selectable as desired; and PA1 wherein, for a second operational state of the vibration roller in which a circular vibration about the roll tire is generated, the first and second driven unbalance shaft are coupled such that the first and second driven unbalance shafts rotate in the same direction and wherein a relative phase position for adjusting a value of the resulting centrifugal force is selectable as desired.
Despite the large number of adjustment possibilities, the inventive vibration roller should have a simple constructive design, a low break-down probability, and a long service life.